U.S. patent number 4,765,293 [Application Number 06/860,506] was granted by the patent office on 1988-08-23 for hybrid internal combustion reciprocating engine.
This patent grant is currently assigned to The Cessna Aircraft Company. Invention is credited to Cesar Gonzalez.
United States Patent |
4,765,293 |
Gonzalez |
August 23, 1988 |
Hybrid internal combustion reciprocating engine
Abstract
A low compression reciprocating internal combustion piston
engine with a prechamber in the head connected to a main combustion
chamber in the piston, the prechamber having an igniter, a pilot
fuel injector and connecting lineal passage; the main chamber
including a fuel injector for mixing the prechamber gases with the
gases being compressed in the cylinder. The engine is a hybrid
having transitional combustion modes from spark-ignited stratified
charge mode at low power, to a spark-assisted compression ignition
at higher power loads, and a strictly compression ignition mode at
maximum power loads.
Inventors: |
Gonzalez; Cesar (Wichita,
KS) |
Assignee: |
The Cessna Aircraft Company
(Wichita, KS)
|
Family
ID: |
25333370 |
Appl.
No.: |
06/860,506 |
Filed: |
May 7, 1986 |
Current U.S.
Class: |
123/275;
123/DIG.7; 123/262; 123/259 |
Current CPC
Class: |
F02B
69/06 (20130101); F02B 23/0639 (20130101); F02B
23/08 (20130101); F02F 3/02 (20130101); F02B
19/1004 (20130101); F02B 23/0624 (20130101); Y10S
123/07 (20130101); F02B 2075/027 (20130101); Y02T
10/125 (20130101); F02B 3/06 (20130101); Y02T
10/12 (20130101); F02B 1/04 (20130101) |
Current International
Class: |
F02B
23/08 (20060101); F02F 3/02 (20060101); F02B
19/10 (20060101); F02B 23/02 (20060101); F02B
69/00 (20060101); F02B 69/06 (20060101); F02B
23/06 (20060101); F02B 19/00 (20060101); F02B
1/00 (20060101); F02B 3/00 (20060101); F02B
3/06 (20060101); F02B 1/04 (20060101); F02B
75/02 (20060101); F02B 017/00 () |
Field of
Search: |
;123/275,262,279,DIG.7,259 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nelli; Raymond A.
Attorney, Agent or Firm: Brown, Jr.; Edward L.
Claims
I claim:
1. A hybrid type reciprocating internal combustion turbine fuel
engine with combined spark ignition, torch-assisted to compression
ignition modes comprising:
a cylinder;
a cylinder head mounted on the cylinder having a substantially
planar inner surface;
exhaust and inlet valves positioned in the head connected to
corresponding exhaust and unthrottled inlet passages;
a piston reciprocally mounted within the cylinder having a top
surface thereon which surface in the top dead center position of
the piston is in close proximity with the inner surface of of the
cylinder head;
a substantially spherical precombustion chamber located in the
head;
a lineal passage tangentially joining the precombustion chamber
with the inner surface of the cylinder head;
a pilot fuel injector means and an igniter means both located in
the precombustion chamber which inject and ignite a precharge;
a main fuel injector means in the cylinder head;
a bowl-shaped recess comprising the main combustion chamber located
in the top surface of the piston in close proximity with the main
injector means in the top dead center position with said lineal
passage tangentially aligned with the main combustion chamber,
whereby the burning gases exiting the precombustion chamber are
directed into the main combustion chamber causing ignition
therein.
2. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, including:
a ramp means located in the top surface of the piston
longitudinally aligned with said lineal passage when the piston is
in the top dead center position.
3. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein there is a timing delay between the pilot
and main injector means.
4. A hybrid type reciprocating internal combustion engine as set
forth in claim 1 wherein the pilot injection precharge ignites by
compression ignition in a medium to high power range.
5. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein the precombustion chamber includes a
temperature insulating liner means which raises the surface
temperature to assist and accelerate combustion.
6. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein the main combustion chamber includes a
temperature insulating liner means which raises the surface
temperature to assist and accelerate combustion.
7. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein the compression ratio of the engine is in
the range of 1:7 to 1:16 and the fuel utilized includes a range of
diesel and turbine fuels.
8. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein the exhaust valve is positioned in
substantially overlapping relation with the main combustion
recess.
9. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein the compression ratio of the engine is in
the range of 1:10 to 1:12 and the fuel utilized includes a range of
diesel and turbine fuels.
10. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein the pilot injector means provides a
substantially constant flow rate per cycle at varying flow rates of
the main injector means.
11. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein the pilot injector means provides a
variable flow rate per cycle at varying flow rates of the main
injector means.
12. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein there are multiple lineal passages
between the precombustion and main combustion chambers, one of
which tangentially joins the precombustion chamber.
13. A hybrid type reciprocating internal combustion engine as set
forth in claim 1, wherein the compression ratio of the engine is in
the range of 1:10, to 1:13 and the fuel utilized includes a range
of diesel and turbine fuels.
Description
BACKGROUND OF THE INVENTION
The invention relates to reciprocating internal combustion engines
fueled by turbine fuels, and more particularly of the type that
operates on a combined stratified, spark-assisted compression
ignition and torch-assisted compression ignition processes utilized
with aviation turbine fuels.
Competition in the world for fossil fuels among various
transportation segments will continue to grow and those fuels that
are manufactured in relatively low quantities are becoming more
expensive and vulnerable to critical shortages and environmental
demands. Among aviation fuels, gasolines have proven to be the most
vulnerable and the additional environmental constraints such as
total elimination of lead as an anti-detonant additive are further
threatening the future availability of high octane aviation gas.
Automotive gasolines may provide a practical alternative to the low
performance range of piston aircraft engines. However, high
performance and high altitude piston aircraft engines must continue
to depend upon high octane aviation gasolines, or an alternative
fuel. There are large worldwide supplies of turbine fuels due to
airline and military requirements which will be maintained in the
foreseeable future. Such fuels offer plentiful supplies with
existing distribution systems and are devoid of liability burdens
associated with automotive gasolines used in aircraft.
Stratified charge engines have been in existence for over 50 years,
as exemplified by the Ricardo Pat. No. 2,191,042. These engines in
isolated cases have successfuly operated with turbine fuels,
however, they have been used in ground transportation applications.
Both stratified and diesel turbine fuel adaptations of the past
represent low specific output engines with limited regard for
economic considerations and their principal objectives being to
meet particular emission standards and multi-fuel capabilities. All
of the prior developments in these areas have failed to produce a
light and efficient high specific output engine capable of
operating on turbine fuels.
A number of prior art patents use a pilot fuel spray which is
ignited by an electrical spark or surface heated element to
establish a flame or stream of hot gases which in turn is used to
ignite a main fuel charge such as typified by Hoffman, U.S. Pat.
No. 2,902,011 and Loyd, U.S. Pat. No. 4,414,940.
The concept of shaping the piston crown to promote swirl as the
piston approaches top dead center is generally taught in the patent
to Yamakawa, U.S. Pat. No. 4,166,436, and applicant's recently
granted U.S. Pat. No. 4,594,976.
SUMMARY OF THE INVENTION
The present invention is directed to a hybrid or convertible
internal combustion engine process which utilizes a stratified
charge Otto cycle during starting, idle and low specific output
operations, while gradually converting to a spark or glow plug
assisted or a non-assisted compression ignition (diesel) mode as
specific engine outputs increase. Transitions from one mode of
operation to another, and degree of said transitions depend on
fuels adopted, combustion chamber compression ratios, degree of
super or turbocharging, coolant temperatures, engine specific
outputs, inlet air temperatures, relative prechamber/main chamber
combustion volumes, prechamber discharge orifice proportions and
other variables. By control of said variables the present invention
combustion process may be adapted to a wide range of
applications.
The precombustion chamber located in the cylinder head includes a
pilot fuel injector and a source of ignition. The prechamber is
connected to the main combustion chamber by means of a passage or
orifice located in such a manner as to induce a swirling airflow
within the prechamber during the compression stroke. During that
swirling airflow, and prior to the piston reaching the top dead
center, the pilot fuel injector discharges fuel into the
precombustion chamber, the mixed fuel and air are then ignited by
the ignition source which initiates the combustion process.
During the starting, idle or low specific power output operations
the prechamber combustion process remains largely or completely
dependent on the stratified charge principles described above.
However, as power increases, with higher chamber surface
temperatures, and higher fuel inputs, the ignition source
dependencies change and the process approaches a spark or glow plug
assisted or a non-assisted compression ignition (diesel) mode.
As combustion develops in the prechamber, temperatures and
pressures increase, and the internal swirl flow is reversed as
combustion gases leave the prechamber through the connecting
passage and flow into the main chamber. The burning gases flowing
through the connecting passage thus impart or enhance the swirling
flow of air within said recess or bowl. As the piston approaches
its top dead center position, the clearances between the piston top
and cylinder head diminish thus forcing the squish air to flow
towards the piston recess along the surface of the piston.
The hot gases, unburned fuel and/or torch flames emanating from the
prechamber further increase the temperature and pressures within
the piston recess and upon main fuel injector discharge of fuel,
said prechamber efflux promotes mixing of fuel with the swirling
air, accelerates precombustion chemical activities and eventually
ignites or assists in the ignition of the main chamber swirling
mixtures. Here again, at low specific power outputs, ignition of
main chamber mixtures are dependent on prechamber efflux gases
and/or torch flame. However, as specific outputs increase, said
dependency decreases and the process gradually approaches a
non-assisted compression ignition mode of operation.
Location of main combustion chamber piston recess substantially
under the exhaust valve reduces heat losses from the main
combustion volume, and complements confinement of main chamber
gases within heated or insulated boundaries as indicated by
combustion and precombustion enhancement provisions. Insulating
inserts or liners with or without catalytic properties over
prechamber, main chamber and associated ramps may be adopted
depending on application, to enhance precombustion chemical
reactions, reduce combustion delay periods, control formation of
deposits, reduce heat losses to engine coolants and lubricating
oils, avoid boundary quenching and reduce ablation or gas erosion
due to excessive heating of light alloy elements.
Pilot and main fuel injections timings may be concurrent or staged
depending again on application parameters such as maximum specific
outputs, engine speeds, fuels used and justifiable complexity of
associated fuel injection systems.
Processes noted above allow the adoption of a relatively low
compression ratio engine capable of producing high specific power
outputs using turbine fuels or other fuels devoid of strict octane
and cetane specific ratings, ideally suited for aircraft use and
capable at operation of relatively high fuel/air ratios (when
compared with standard stratified or compression ignition engines),
thus reducing engine size, weight, installation volume,
manufacturing cost and reducing induction air supercharging or
turbocharging demands.
Adoption of spark or glow plug ignition assistance provisions, hot
insulated combustion chamber liners and prechamber torch ignition
of main combustion chamber reduces combustion delay periods thus
limiting the amounts of raw fuel present at point of ignition, and
in turn yielding conservative combustion pressure rise rates and
peak pressures. These conditions control knock and reduce engine
structural demands.
It is therefore the principal object of the present invention to
provide an aircraft reciprocating piston engine capable of
operating on turbine fuels.
Another object of the invention is to provide a reciprocating
piston engine other than aircraft applications capable of operating
with fuels devoid of octane ratings or cetane specific rating
requirements.
Another object of the present invention is to provide a lightweight
high specific output piston engine capable of operating with
turbine fuels at relatively low compression ratios and relatively
high fuel/air ratios.
A further object of the present invention is to provide an improved
piston engine capable of operation on spark-ignited stratified
combustion at low specific output over a wide range of fuel/air
ratios and transitioning to a spark-assisted compression ignition
or non-assisted compression ignition mode at higher specific
outputs but capable of efficient operation at fuel/air ratios
higher than normally practical with traditional non-assisted
compression ignition engines.
Another object of the present invention is to provide an improved
piston engine with low specific air consumption and throttleless
operation thereby extending the altitude capabilities of current
technology turbochargers.
Further objects and features of the invention will become apparent
from the following detailed description taken in connection with
the accompanying drawings which form a part of this
specification.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of the engine of the present invention
with the cylinder and head not shown in detail, to better view the
combustion chambers;
FIG. 1A is a perspective view of the piston only showing a modified
form of the main combustion chambers;
FIG. 2 is a top plan view of the piston with the precombustion
chamber and its related components shown in dotted line;
FIG. 3 is a sectional view taken along line 3--3 of FIG. 2,
illustrating the cylinder, cylinder head and piston in the top dead
center position;
FIG. 4 is a sectional view taken along lines 4--4 of FIG. 5;
FIG. 4A is a similar sectional view of a modified form of
precombustion chamber;
FIG. 5 is a sectional view through the precombustion chamber and
cylinder;
FIG. 5A is a similar sectional view of a modified form of
precombustion chamber;
FIG. 6 is a symbolic illustration of various air, fuel and gas
flows during compression, at top dead center and at the initiation
of th expansion stroke; and
FIG. 7 is a perspective view of the FIG. 1A piston top surface
illustrating the various air and gas flow paths at the top dead
center position.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The hybrid engine of the present invention is generally described
by reference numeral 10, as seen in FIG. 1. While the engine is
only shown with a single cylinder 15, it is capable of utilizing
any number of cylinders in any cylinder arrangement pattern.
Various parts of the engine are conventional and well-known in the
art and are therefore not described in detail.
The engine includes a piston 11, reciprocally mounted within a
cylinder 15, closed at its upper end by a cylinder head 34, as best
seen in FIGS. 3, 4 and 5. Located in the cylinder head 34 are a
pair of conventional inlet and exhaust valves 12 and 13,
respectively, located in inlet and exhaust passages 14 and 32
(shown in dotted line in FIG. 1). Passing through the inner surface
36 of cylinder head 34 is a main fuel injector 25, as best seen in
FIGS. 2, 3 and 4. Also located in cylinder head 34 is a
precombustion chamber or prechamber 19 which connects with the
interior of the cylinder through a lineal passage 20, as best seen
in FIGS. 2 and 4. The cross sectional area of passage 20 must be
sufficiently small to create a high enough velocity in chamber 19
during the compression stroke to maintain a high rate of fuel
emulsification, yet not too strong to blow off the fire kernel.
Also located in precombustion chamber 19 is a spark plug 24 and
pilot fuel injector 22. Both the pilot injector 22 and the main
injector 25 are controlled by conventional means not shown in the
drawings. Chamber 19 is substantially spherical, or a figure of
revolution, with lineal passage 20 tangentially intersecting
chamber 19 so that gases entering through passage 20 create a
swirling flow.
Located in the top surface 38 of the piston is main combustion
chamber recess or bowl 16 which may be slightly offset from the
center of the piston. Lateral passage 20 is tangentially aligned
with recess 16 when the piston 11 is close to its top dead center
position, as illustrated in FIGS. 2, 4, 5 and 7.
FIG. 1A illustrates a slightly modified piston 11 with a tangential
ramp 17 entering recess 16' which is longitudinally aligned with
lineal passage 20 when piston 11' is in its top dead center
position.
At the top dead center position, also referred to as TDC, the
clearance between the top surface of the piston 38 and the inner
surface 36 of the head is reduced to practical mechanical limits so
that substantially all of the available combustion volume at TDC is
basically precombustion chamber 19, lateral passage 20, main
combustion chamber or recess 16 and ramp 17 when applicable.
FIGS. 4 and 5 illustrate a slightly modified form of the invention
wherein the precombustion chamber 19 is provided with a liner 40.
The liner is temperature-insulated material intended to raise the
surface temperature for the purpose of promoting combustion.
Various types of liner materials can be used which not only affect
the chemical process of combustion, but also accelerate combustion,
reduce combustion delays, accelerate evaporation of the fuel
impinging on the liner surfaces, as well as control combustion
deposits. The liner material may be an alloy incorporating elements
such as nickel-chromium and copper. The liner material can also be
a ceramic compound with elements such as zirconium which promote
combustion via catalytic enhancement.
FIGS. 4A and 5A illustrate a modified form of precombustion chamber
19' which has multiple lineal passages 20' connecting to the main
combustion chamber which provides a different flame discharge
pattern.
DESCRIPTION OF THE OPERATION
The engine 10 operates in accordance with a four-stroke cycle. On
the first stroke, piston 11 moves downward with intake valve 12
open and exhaust valve 13 closed. The downward movement of piston
11 cases air to flow through the normally unthrottled or
unrestricted intake passage 14 into the cylinder 15. Airflow into
the cylinder is promoted by atmospheric pressure or conventional
supercharging pressures acting on the induction air entering
passage 14. On the second stroke of the cycle, air inlet valve 12
is closed, exhaust valve 13 remains closed, and piston 11 moves
upward to compress the air in cylinder 15, as illustrated by the
COMPRESSION STROKE in FIG. 6. As the piston 11 moves upward during
the compression stroke, compression air is forced through lineal
passage 20 into precombustion chamber 19, introducing a swirling
airflow pattern as indicated by the arrows in FIG. 6.
As piston 11 approaches its top dead center position, pilot fuel
injector 22 injects a spray 23 into the swirling compressed gases,
as illustrated in the TDC position of FIG. 6. The optimum timing at
which pilot fuel injection occurs would vary for each application,
depending upon the operating conditions and the particular engine
size. The amount of fuel injected during each individual cycle may
be constant or may vary depending upon different applications.
Occurring at substantially the same time as pilot injection,
igniter spark plug 24 is caused to fire thereby beginning ignition.
Other ignition sources such as electrically heated glow plugs, not
shown, could also be utilized during engine start-up and initial
warm-up, while the glow plug would remain heated by combustion heat
with or without the assistance from an electrical source. As the
pilot fuel spray begins to burn, the expansion of the burning gases
causes a reversal in flow direction, as indicated by arrows 27 in
FIG. 6. The burning gases or torch flame 27 are now directed
tangentially into main combustion recess 16 causing a swirling
action of the gases, as indicated by arrows 28 in FIG. 7.
As the piston 11 approaches its top dead center position, the
clearance between the top surface 38 of the piston and the inner
surface 36 of the head rapidly diminishes in an area generally
referred to as the "squish volume". The gases in this rapidly
decreasing volume will flow into main combustion chamber 16. This
last-mentioned flow likewise induces a swirling flow and mixing
action within recess 16. The squish volume gases entering recess 16
are caused to intersect and mix with the burning gases 27 flowing
from the prechamber 19 while they together flow into the main
combustion recess 16.
A main fuel spray 29 is injected into the main combustion recess 16
through main fuel injector 25. The timing of main fuel injection
may be concurrent with the pilot fuel injection on engines of low
specific output or low compression. However, generally, main fuel
injection will be timed after pilot injection, well after
prechamber combustion is under way. Delayed main fuel injection
allows the fuel to burn with minimum delay within the strong
swirling preconditioned air in piston recess 16, practically as it
emerges from injector 25. Since no fuel is allowed to accumulate
within recess 16, the combustion process that follows is smooth and
conducive to low peak combustion gas pressures.
Under certain conditions of low power or with a cold engine, pilot
and main fuel injection sprays may contact the surfaces of the
prechamber 19 and recess 16, thus introducing a combustion delay
factor, and during these circumstances, burning of deposited fuels
will largely depend on fuel evaporation rates from those surfaces.
Both pilot and main injectors 22 and 25 inject sprays directly into
combustion volumes 19 and 16, and thus provide a wide range of
fuel/air ratios.
The modified piston 11' of FIG. 1A directs the burning gases 27
down an entry ramp 17 for a similar tangential entry into main
chamber 16', as seen in FIG. 7.
From the foregoing statements, summary and descriptions in
accordance with the present invention, it is understood that the
same are not limited thereto, but are susceptible to various
changes and modifications as known to those skilled in the art, and
we therefore do not wish to be limited to the details shown and
described herein, but intend to cover all such changes and
modifications which would be encompassed by the scope of the
appended claims.
* * * * *